1. Field of the Invention
This invention relates to neurostimulation, and more particularly relates to an apparatus system and method for neurostimulation by high frequency stimulation.
2. Description of the Related Art
Directly stimulating bioelectrically excitable tissue may be beneficial as a therapeutic tool. For example, neurostimulation may be used for restoring function in cases of neural injury or disease. Neurostimulation as used herein refers to the stimulation of electrically excitable tissues of living things. This can include, for example, the human tissues of the brain, heart, muscle, and nervous system.
Two methods of neurostimulation are the application of pulsed electrical currents directly to tissue through electrodes implanted within tissue and the indirect application of electrical currents through the body surface.
Directly applied electrical currents applied to tissue are known to affect the membranes of excitable cells, causing a depolarizing effect that can lead to a cell action event that depends on its type and biological function. The pulsing of currents is sometimes needed to prevent accommodation to current flows and to fulfill certain physiologic conditions that enables electricity to be effective. Direct application of currents may have the disadvantage of requiring invasive techniques, such as inserting probes or wires into the body.
It is also possible to apply electrical currents to the body surface where they diffuse in the volume conductivity of tissue and attenuate according to well known laws. These currents can also stimulate near-surface nerves and muscle tissues to some degree, but cannot reach deeper tissues because of high electrical losses in tissue and the rise in the needed current levels to above those that would cause electrical shock and tissue damage. It is also difficult to specifically stimulate a particular area of tissue without stimulating surrounding areas.
The strong diffusion of electrical current in tissues from surface electrodes means that specific stimulation of a given nerve or nerve fiber within a bundle is difficult. There is a tendency for electrical currents applied to the body surface to broadly stimulate in undesirable ways. Implantable electrodes overcome these problems but are invasive and suffer from the undesirable need to either run wires through the skin or work with relatively bulky implanted power systems that run on batteries or are powered by external radiofrequency (RF) powering techniques.